1. Field of the Invention
The present invention relates to a high electron mobility transistor, an epitaxial wafer, and a method of fabricating the high electron mobility transistor.
2. Related Background Art
Patent Literature 1 discloses a transistor having an annular gate electrode. An undoped AlN layer (50 nm thick), undoped GaN (1 μm thick) layer, and undoped Al0.2Ga0.8N layer (25 nm thick) are sequentially grown on a sapphire substrate by molecular beam epitaxy.
Patent Literature 2 discloses a transistor having normally-off characteristics. The transistor has a GaN-based semiconductor layer grown on a GaN-based single crystal substrate. The GaN-based single crystal substrate constitutes an electron channel layer while the GaN-based semiconductor layer constitutes an electron supply layer. A primary growth surface of the GaN-based single crystal substrate is m-plane, and a primary growth plane of the GaN-based semiconductor layer formed on the GaN-based single-crystal substrate is also the m-plane. The m-plane (nonpolar plane) produces no piezoelectric field, leading to suppression of creation of a two-dimensional electron gas layer at the heterojunction when no gate voltage is applied.
Non-patent Literature 1 discloses an estimation of piezoelectric field.    Patent Literature 1: Japanese Patent Application Laid-Open No. 2005-033073    Patent Literature 2: Japanese Patent Application Laid-Open No. 2008-311533    Non-patent Literature 1: JJAP, vol. 39, 413, (2000)